Time, as told by a sundial

The Importance of Sundials in Creating Time

Time, as told by a sundial
Nick Somoski's image for:
"The Importance of Sundials in Creating Time"
Caption: Time, as told by a sundial
Image by: Walter Sanford
© June 23, 2002

The early intelligence of mankind is perfectly exemplified in the sundial, an ancient creation that has stood the test of time - literally - through its innovative precedence and quintessential significance. It allowed man to tell time for the very first time, and today, it stands as more than just a garden ornament: the sundial is the basis for the modern-day clock and the model of necessary technology that today's society could not live without.

The history behind the sundial is tremendous, and the "historical" sundial goes as far back as Egyptian times, about 1500 BC, in the form of "shadow clocks." Before that, humans (around 3000 BC) were reading shadows casts by obelisks - tall, thin stone towers with a pointed top that cast large shadows brought forth by the sun. In these early instances, it was the sun that allowed humans to tell time, and they eventually made the concept into the first man-made analog clock.

While obelisks could only tell morning from afternoon, and while shadow clocks could only split the day into 4 parts, sundials were able to tell time hour to hour. The earliest design of this sundial is said to have originated by the Babylonians sometime between 1500 and 700 BC. The Greeks perfected the design; it was horizontal, aligned directly with the earth's axis from pole to pole. Along with the design, they refined the geometry involved to make the shadows match up at each hour, which included exact positioning and determining lines of longitude and latitude, as to match up exactly with the north and south pole (and, therefore, the positioning of Earth's axis at different points of the year). 

These sundials were nodus-based, meaning the shadow was made by a slanted, pointed "extension," something like a rod or sharp tip (also called a gnomon) that sat in the middle. As the sun moved across the sky throughout the day, a shadow would move around the base in the same fashion the hands of a clock would. The gnomon was what was positioned according to Earth's axis; if it was not perfectly lined with the axis, the time would be slightly off, which was often the case. 

Eventually, hour lines were carved into sundials, and later sundials (and modern ones) were made with the hour lines already depicted. While the sundial no longer had to be exactly lined with the poles, it resulted in numerous problems. Because sundials tell solar time within each local area, it was not a uniform mechanism. The time in one city would be different, for example, from the time in a city that was 100 miles west (this problem has since been corrected with the implementation of time zones).

As well, because the rotation of the Earth is not precisely circular, the time day to day (and especially year to year) would never be the same, and constant adjustments had to be made.

As the Romans and other cultures adopted the sundial, they also made it their own. The ways in which time was told on a sundial were differed between designs. Holes carved into sundials could allow for a beam of light to move around the base, shifting the sundial from shade-based to light-based. The size of the sundials decreased as the portability increased.

The Renaissance brought new designs for both horizontal and vertical sundials. Mechanical analog clocks were first created in the early 1000s, and time officially began to be measured in hours. A new invention, the pendulum, was first discovered by Italian astronomer Galileo Galilei in the 1500s and corrected one major problem of the sundial: the constant error of time, which was minimized to a mere seconds each day. Instead of depending on the movement of the sun, the pendulum relied on the movement of the earth and gravity to create a "swing" that would move back and forth and slightly change direction with each pass to reflect the change in time.

By the 1700s, clocks and watches were invented and eventually made widely available. Their innovation continues today, as the majority of clocks are now digital. Although sundials are still around today, they are no longer needed because of modern technology, but that is no reason to rule out their significance to human kind.

Regardless of the manner in which time is told nowadays, it is able to be told because of the original time-telling device, the one on which all further devices were based: the sundial. Because of the sundial, time was able to be kept in a relatively-systematic matter for the first time. Because of it, day could be separated from night; sunrise and sunset could be predicted, and measurement in hours, minutes, and seconds was enabled. The true purpose of the historic sundial is one that could never be discounted.

More about this author: Nick Somoski

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